This invention relates generally to the field of an exhaust control method and apparatus and more precisely, but not by way of a limitation, to a new and improved motorcycle exhaust apparatus.
Internal combustion engine exhaust noise muffling or sound suppression has been accomplished in the prior art by either absorbing the sound pressure waves in some fashion or by canceling the waves with other waves from the same source while effecting a decrease in the velocity of the exhaust gases. Exhaust sound suppression produced a back pressure of the exhaust on the engine which adversely affected the engine's performance, reliability and efficiency, and which required that the exhaust flow resistance be made as small as possible. An increase of 1 psi in exhaust back pressure decreased the maximum power output of an engine by an average of 11/2 percent. Back pressure was especially critical in muffing the exhaust of a motorcycle two-cycle engine, which operated at full load more frequently and was more sensitive to the exhaust control. With the adoption of the government regulations establishing maximum permissive noise levels for motorcycles, the need for an efficient motorcycle exhaust control apparatus became even more acute.
Typical prior art motorcycle exhaust muffling devices were illustrated and described in U.S. Pat. Nos. 2,492,784 and 3,482,648. Packing an annular area between an inner perforated conduit and a muffler shell with a packing of sound absorbing material was disclosed in U.S. Pat. No. 1,844,105, but only random flow and not a selected portion of the exhaust flow was directed into contact with the sound absorbing material. U.S. Pat. No. 3,434,280 disclosed a tunable motorcycle exhaust expansion chamber for reflecting a portion of the exhaust pressure wave to tune the chamber and contain the fresh charge of air-fuel mixture in the cylinder for increasing engine efficiency and power, but lacked any sound attenuating or muffling means. The disclosure of U.S. Pat. No. 1,611,475, employed a plurality of nozzles positioned in a series to reflect portions of the sound waves flowing therethrough for canceling other portions of the sound waves while U.S. Pat. No. 3,414,078 provided a tuned resonance muffler in which a standing wave was created in a closed chamber to combine with the exhaust flow for effecting a cancellation of the sound waves.